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UBC Theses and Dissertations

The optical response of silicon thin-films grown by ultra-high-vacuum evaporation Moghaddam, Saeed


Conventional forms of silicon thin-film, prepared through the use of a plasma, offer a variety of attractive electronic properties but are prone to an instability. Hydrogen atoms are believed to be the source of the instability. Accordingly, experimental collaborators at the National Research Council of Canada employed ultra-high-vacuum evaporation to prepare thin-films of silicon on optical quality fused quartz substrates, which allow for a great deal of atomic species control during the growth process. The optical properties associated with these ultra-high-vacuum prepared forms of silicon thin-film are examined. In particular, through experimental measurements of the specular reflectance spectrum at near-normal incidence and the regular transmittance spectrum at normal incidence, the spectral dependence of the optical functions is resolved for eleven silicon thin- films, deposited at different growth temperatures. Generally, the refractive index increases in response to increases in the growth temperature. The optical absorption spectral dependence is also observed to exhibit a fundamental transition in its behavior with increases in the growth temperature. These observations are related to the changes that occur in the crystalline volume fraction accompanying increases in the growth temperature. A detailed quantitative uncertainty analysis is also performed. Drawing upon X-ray diffraction results, a placement of these silicon thin-films into the overall silicon thin-film continuum is then performed. Raman spectral results are then correlated with the refractive index's spectral dependence. The Raman spectrum of a given silicon thin-film allows for a probe of the order, correlating the Raman results with the optical function results providing one with the opportunity to probe how disorder influences the optical functions. All measures of order suggest that the order increases in response to increases in the growth temperature. Finally, the device implications of these results are explored, with a focus on photovoltaic device applications. It is concluded that this particular form of silicon thin- fil is a promising material for use as the absorbing media within solar cells, offering an enhancement in the absorption which is greater than that offered by conventional plasma prepared silicon thin-films.

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